Graduate Spotlight: Rebecca Shirk
Expected Graduation: Spring 2013
Degree Objective: Ph.D. in Plant Biology
Other Degrees: B.A. in Biology, B.A. in East Asian Studies
Rebecca Shirk, a plant biology doctoral student, has firsthand experience fighting invasive plant species – with a backpack sprayer while plodding through marsh in Ohio’s Cuyahoga Valley National Park.
“I spent a summer working for the National Park Service on an invasive species control team,” said Shirk. “Our job was to monitor and remove invasive plants throughout the park.”
These days, Shirk has moved to the laboratory to combat invasive vegetation in the University of Georgia’s Department of Plant Biology. Her plant genetics research is funded by the National Science Foundation as one part of the Partnership for International Research and Education. The UGA PIRE program allows U.S. and Chinese researchers to collaboratively map the genetics of introduced plant species.
“I knew I wanted to study invasive plants, and the idea of having an international research component added to my dissertation was very appealing,” said Shirk.
Shirk is investigating the colonization patterns of a common weed native to the United States – Geranium carolinianum – in China. Commonly known as the Carolina cranesbill, G. carolinianum was recently introduced to China where it has largely taken root in areas with disturbed soil, such as urban areas and farmland, and developed a resistance to common herbicides.
Shirk has traveled throughout the Southeast and China to collect native and introduced plant samples. Back in the lab, she compares the plant samples’ genetic variations. The Carolina cranesbill’s genetics reveal how it has colonized and adapted to a foreign environment.
“I’m using population genetics to trace the introduction and invasion history of this species to understand how it has been moved around China and how this might affect its success,” she said. “I’m also looking at different aspects of the plant’s physiology to identify what characteristics affect its invasiveness.”
Population genetics measures the frequency of genetic traits and genetic diversity found in an entire population. Using this type of analysis, Shirk can trace the Carolina cranesbill’s movement, showing her where the first plants originated and how it migrated across China.
“Right now, it looks like there was a single introduction point around Shanghai, and its range has since expanded to the south and west,” said Shirk.
According to Shirk, introduced species have less genetic diversity than native species, which leads to a more homogenous population. The genetic homogeneity of invasive plant species means different management strategies.
“Species that are more homogenous genetically are probably easier to control, because they will be unable to escape or evolve resistance to whatever control measures you use,” she said. “In some species, identification of native source populations can be useful in finding native predators or herbivores that can be introduced as biological control agents.”
In addition to the Carolina cranesbill, mapping the weed’s invasive course may help control other introduced plants.
“If we can identify the entry point of an invasive species, it makes it easier to prevent future introductions,” she said. “G. carolinianum was probably introduced unintentionally – as a seed contaminant – and it’s likely there are other species that are being unintentionally introduced along the same routes.”
Ultimately, Shirk hopes her graduate work on invasive plant colonization will slow the spread of non-native plant species worldwide.
“In understanding the genetics behind successful invasions, we should be better equipped to develop effective control and management programs,” she said. “It will also help us be better at identifying high-risk species before they are introduced.”
Shirk has two years left at UGA before she finishes her doctoral research. After graduation, she will likely continue her career in academia or at a government agency like the U.S. Forest Service or the U.S. Department of Agriculture.
Story by Ben Benson